Process for producing alkyltin compounds



United States atent O 3,211,769 PROCESS FOR PRODUCING ALKYLTIN COMPOUNDS1 Lloyd H. Brown, Crystal Lake, Ill., and Jimmy W. Hill, Olean, N.Y.,assignors to The Quaker Oats Company, Chicago, 11]., a corporation ofNew Jersey N Drawing. Filed Sept. 4, 1962, Ser. No. 221,338 11 Claims.'(Cl. 260-429.7)

This invention relates to a new and improved process of preparingalkyltin compounds by reacting an alkyl halide and a magnesium-tin alloyin the presence of a cyclic ether solvent.

Heretofore, commercial processes for producing alkyltins have involvedthe use of the conventional Grignard process which required three orfour operations under rather strenuous processing conditions, such ashigh temperatures, thus resulting in high processing costs. Also, insome of these processes, raw material costs have been higher than isdesirable. One particular prior art process has overcome some of thesedisadvantages by reacting alkyl halides and a magnesium-tin alloy in thepresence of inert reaction solvents such as cyclohexane. However, thelatter process has the disadvantage that it is not suitable for thepreparation of higher alkyltin compounds such as butyltin compounds.

It is an object of this invention to provide a process for producinghigher alkyltin compounds such as butyltin as well as the lower alkyltincompounds.

Another object of the invention is to provide a process for convertingrelatively low cost raw materials into alkyltin compounds with aresulting relatively small amount of unconverted raw materials.

A further object of the invention is to provide a process for producingalkyltin compounds at relatively low temperatures of reaction and with aminimum of processing steps.

In accordance with the invention these objects are accomplished byreacting an alkyl halide with a magnesiumtin alloy, preferably Mg Sn, inthe presence of a special coordinating reaction solvent to producehalogen-free alkyltin compounds.

We have found that by use of a cyclic ether solvent selected from thegroup consisting of tetrahydrofuran, tetrahydropyran, and certainsubstituted derivatives or mixtures thereof, the reaction between alkylhalides and magnesium-tin alloys proceeds under relatively mildconditions. The product obtained, depending upon the proportions ofreactants, is a mixture of alkyltin compounds which are useful for avariety of purposes.

While we do not wish to be bound by any theoretical explanation of ourdiscovery, we believe, based on experimental observations, that thespecial cyclic ether solvents coordinate with and remove from themagnesiumtin alloys, certain intermediate products which are believed toprevent a satisfactory reaction between the alloys and the alkylhalides. The cyclic ether solvents employed in this invention have beenfound to be unique in promoting reaction between the alkyl halides andthe magnesiumtin alloys and particularly with respect to reaction ofhigher alkyl halides such as butyl chloride. Other commonly usedsolvents such as cyclohexane and other hydrocarbons have been employedas an inert medium for reaction of lower alkyl halides such as ethylbromide and magnesium-tin alloys. The products produced with the use ofthese solvents are principally alkyl tin halides together withappreciable amounts of tetraalkyltin compounds. Reaction of higher alkylhalides such as butyl chloride with magnesium-tin alloys to form. butyltin compounds cannot be accomplished with these inert solvents. Incontrast, the cyclic ether solvents employed in the present inventionpromote reaction between the magnesiurn-tin alloys and higher alkylhalides such as butyl chloride as well as the lower alkyl halides.Moreover, with the use of the cyclic ether solvents of this inventionthe principal products produced from the reaction are polymeric typealkyltin compounds substantially free of halogens. The tin compoundsproduced in accordance with the invention can be represented by theformula:

wherein R is an' alkyl radical having from 2 to 8 carbon atoms and n iszero or a positive integer.

Only relatively small amounts, if any, of tetraalkyl tin compounds areproduced in the process of this invention.

The unique suitability of the specified cyclic ether solvents for thepurpose of the invention is apparent also when compared with othercoordinating solvents of more highly basic nature than the cyclic ethersolvents. Thus, for example, pyridine and similar highly basiccoordinating solvents, when employed in carrying out the process of theinvention, generally lead to the formation of unknown, colored productswhich do not yield the desired useful alkyltin compounds.

The cyclic other solvents which have been found unique in promotingreaction between the alkyl halides and the magnesium-tin alloys to formcompounds of the type designated in the above formula includetetrahydropyran, tetrahydrofuran, alkyl substituted tetrahydrofurans andtetrahydropyrans in which the alkyl substituent is attached to a carbonatom not adjacent to the oxygen atom, and mixtures of the foregoing. Thealkyl substituent can be an alkyl radical containing from 2 to 8 carbonatoms.

Reaction of the alkyl halides and the magnesium-tin alloys is preferablyconducted at approximately the reflux temperature of the solventemployed which in the case of tetrahydrofuran is 66 C. andtetrahydropyran 83 C. Lower temperatures can be employed for thereaction but are less preferred since the reaction rate is slowernecessitating longer reaction times. Higher reaction temperatures canlikewise be employed particularly when it is desired to produce largeramounts of the dimer tin compounds (n=0 in Formula I) since highertemperatures favor the production of these compounds. In general, thereaction can be carried out over a very wide range of temperatures suchas from about 60 to about C.

It is preferred, but not essential, to employ catalysts in the reaction.Suitable catalysts include metallic mercury and the halides such as thechlorides, bromides and iodides of mercury or cobalt. A particularlypreferred catalyst is mercuric chloride.

Suitable alkyl halide reactants include alkyl chlorides, bromides oriodides. The alkyl group can range from ethyl to octyl or higher.

In a preferred embodiment of the invention a molar excess of the alkylhalide is reacted with the magnesiumtin alloy by mixing the alkyl halidewith an excess of the special reaction solvent and adding the mixtureincrementally to a reaction vessel containing the alloy and metalcatalyst in finely ground form and protected by a nitrogen atmosphere.The amount of reaction solvent must be suflicient to keep the reactionmixture fluid throughout the reaction. The reaction mixture is heated ata refluxing temperature until the reaction is complete as evidenced bythe absence of unreacted alloy. The time of reaction ranges from aboutan hour to about 24 hours depending on the temperature applied to thereaction and the mole ratio of alkyl halide to' the alloy. The reactionmixture is then washed with a dilute aqueous mineral acid to removemagnesium halides, and the resulting aqueous phase containing magnesiumhalide and the resulting organic phase containing the alkyltin compoundsare separated by conventional means. The product of the reaction of theinvention is generally a mixture of alkyltin compounds which are usefulintermediates in the preparation of highly valuable tin compounds.

With the use of low molar ratios of alkyl halide to magnesium-tin alloy,i.e. 5:1 or lower, the n in Formula I approaches zero so that theprincipal products obtained are dimer compounds, bis-(trialkyltin). Withthe use of high molar ratios of alkyl halide to magnesium-tin alloy theprincipal products are polymers wherein n in Formula I is a positiveinteger. Molar ratios of alkyl halide to magnesium-tin alloy can rangefrom 2:1 to 8:1 or more.

The bis-(trialkyltin) compound can be reacted with hydrochloric acid byconventional means to form the chloride which can then be hydrolyzed, ifdesired, to form trialkyltin oxide. One such compound, namelytributyltin oxide, finds widespread use in fungicides, bacteriostats andgermicides.

The polymer tin products (nzpositive integer in Formula I) can bedirectly oxidized with atmospheric oxygen and at room temperature toform dibutyltin oxide. This material is useful as an intermediate in thepreparation by conventional means of such compounds as dialkyltindiacetate, dilaurate, maleate, sulfide, dichloride, and mercapto esters,as well as tetraalkyltin, etc. Such means of preparation of thederivatives and their applications are described in ChemicalEngineering, vol. 65, No. 16, pages 78-82.

The invention will be further illustrated but is not limited by thefollowing examples in which the quantities are stated in parts by weightunless otherwise indicated:

Example 1 The magnesium-tin alloy, Mg Sn, was prepared by heating withagitation 72 parts of tin shot and 28 parts of magnesium turnings at 800C. for 15 minutes in an iron crucible and nitrogen atmosphere. A mixtureof 265 parts of anhydrous tetrahydropyran and 333 parts of butylchloride was prepared. About 22 parts of the mixture and about 2 partsof ethyl bromide (hastens initiation of reaction but is not essential)was introduced into a reaction vessel having a nitrogen atmosphere andcontaining a finely ground mixture of 74.3 parts of the Mg Sn alloy and1.5 parts of mercuric chloride. Heat was applied to the vessel to effectrefluxing at a temperature of about 8386 C. and when the reaction hadbegun, as evidenced by turbulence and the formation of gray particles,the remaining tetrahydropyran-butyl chloride mixture was added dropwiseover a period of about one hour. The refluxing was continued for anadditional 6 hours and 45 minutes after which the mixture was cooled toabout 5 C. Three hundred parts of 3% aqueous hydrochloric acid were thenadded to the reaction vessel, dropwise at first, with agitation. Theaqueous and organic phases which formed were separated. The organic partwas washed three additional times with 300 parts of 3% aqueoushydrochloric acid to insure complete removal of magnesium chloride. Theaqueous part was washed once with Skellysolve F (a hydrocarbon productof the Skelly Oil Company of El Dorado, Kansas) to recover additionalorganic product which was combined with the original washed organicportion. The organic portion was distilled, at atmospheric pressure atfirst and then with vacuum gradually applied, to remove all traces oflow boiling impurities. The final distillation temperature was 100 C.and the final pressure was 18 mm. of mercury. The product residue was114.1 parts of a pale green, slightly viscous liquid having a tinanalysis of 45.94% by weight using the analytical method of Gilman andKing, J.A.C.S., vol. 51, page 1213. The tin analysis of 45.9% indicatesthat the principal product was a polymeric product. A conversion of98.2% by weight based on the weight of tin in the alloy, was obtained inthis example in which the mole ratio of butyl chloride to themagnesium-tin aly was 8: 1.

Example 2 The procedure of Example 1 was essentially repeated with theexception that the reaction was carried out in a Parr bomb, the reactiontime was eight hours and the reaction temperature was in the range105-145" C. The product had a tin analysis of 41.50% by weight and theconversion was 92.3% by weight. The tin analysis indicates that theprincipal product was the dimer, bis-(tributyltin).

Example 3 The procedure of Example 1 was essentially repeated with theexception that the reaction time was two hours and the refluxingtemperature was in the range 83-86 C. The product had a tin analysis of45.40% by weight and the conversion was 74.8% by weight.

Example 4 The procedure of Example 1 was essentially repeated with theexception that the mole ratio of butyl chloride to Mg Sn was 5:1, thereaction time was 24 hours, and the refluxing temperature was in therange 8391 C. The product had a tin analysis of 41.76% by weight and theconversion was 88.9% by weight.

Example 5 The procedure of Example 1 was essentially repeated with theexception that the reaction solvent was tetrahydrofuran instead oftetrahydropyran, the mole ratio of butyl chloride to Mg Sn was 3:1, thereaction time was 12 hours, and the refluxing temperature was in therange 66-77 C. The product had a tin analysis of 38.99% by weight andthe conversion was 50.3% by weight.

Example 6 The procedure of Example 1 was essentially repeated with theexception that the mole ratio of butyl chloride to Mg Sn was 2:1, thereaction time was 24 hours, and refluxing temperature was in the range83-92 C. The product had a tin analysis of 37.24% by weight and theconversion was 38.0% by weight.

Example 7 The procedure of Example 1 was essentially repeated with theexception that the reaction solvent was a mixture of 60 partstetrahydropyran and 40 parts tetrahydofuran, the reaction time was fourhours, and the refluxing temperature was in the range 78-83 C. Theproduct had a tin analysis of 45.48% by weight and the conversion was byweight.

Example 8 The product mixture of Example 7 was oxidized to dibutyltinoxide. Air was blown very slowly into a mixture of 37.08 grams of theExample 7 product and milliliters of Skellysolve B for 24 hours. A whiteprecipitate of butyltin oxide (21.62 grams) was separated by filtration,washed, and then dried at 60 C. in a vacuum oven. The product had a tinanalysis of 47.05% by weight which compared favorably with the 47.68%theoretical tin content of dibutyltin oxide. Further proof that theproduct was dibutyltin oxide was demonstrated by its known reaction withhydrochloric acid to form dibutyltin dichloride, Bu SnCl To 12.48 gramsof the above dibutyltin oxide in a beaker, there was added an excess ofconcentrated hydrochloric acid at room temperature. After 15 minutes,the oily material which separated was extracted with Skellysolve B.After separation, washing and drying, the solvent was stripped. Thereremained 13.9 grams of crude Bu SnCI which had a melting point of 3538C. When recrystallized from Skellysolve B, it had a melting point of41.0- 41.5" C. The melting point was not depressed when mixed with anequal weight of pure known dibutyltin dichloride. An infrared curve ofthe product compared favorably with the infrared curve of puredibutyltin dichloride. The product analyzed 39.28% by weight of tin and23.35% by weight of chlorine as compared respectively to the theoreticalvalues of 39.07% and 23.34% of Bu SnCl Example 9 The procedure ofExample 1 was essentially repeated with the exception that 300 parts ofpyridine replaced the tetrahydropyran as reaction solvent. After eighthours at 85 C., the reaction system was found to be a black, tarry massfrom which no useful products were obtained.

Example 10 The procedure of Example 1 was essentially repeated with theexception that 300 parts of 3-methyltetrahydrofuran replaced thetetrahydropyran as reaction solvent. The results obtained were similarto those of Example 1.

Example 11 The procedure of Example 1 was essentially repeated with theexception that 300 parts of S-butyltetrahydropyran replaced thetetrahydropyran as reaction solvent. The results obtained were similarto those of Example 1.

The present invention provides an improved process for producing usefulalkyltin compounds. A critical feature of the invention is the use ofthe specified cyclic ether solvents which have been found unique inpromoting the formation of alkyltin compounds. As indicated, the cyclicether solvents of the invention permit the production of alkyltincompounds of the type designated by Formula I by reaction ofmagnesium-tin alloys with alkyl halides including higher alkyl halidessuch as butyl chloride and the like. This is in contrast to other inertsolvents known in the art which do not permit reaction between thehigher alkyl halides and magnesium-tin alloys and which in the case ofthe lower alkyl halides favor the production of alkyltin halides. Theprocess of the invention can be carried out using relatively mildreaction conditions with the obtainment of high yields of desired tincompounds.

Those modifications and equivalents which fall within the spirit of theinvention and the scope of the appended claims are to be considered partof the invention.

We claim:

1. A process for producing halogen-free alkyltin compounds whichcomprises reacting at a temperature not substantially above 150 C. analkyl halide with a magnesium-tin alloy in the presence of a reactionsolvent selected from the group consisting of tetrahydrofuran,tetrahydropyran, alkyl substituted tetrahydrofuran and tetrahydropyranin which the alkyl substituent is attached to a carbon atom not adjacentto the oxygen atom, and mixtures thereof.

2. A process according to claim 1 wherein said halide is a chloride.

3. A process according to claim 1 wherein there is employed a catalystselected from the group consisting of metallic mercury, the inorganichalides of mercury and the inorganic halides of cobalt.

4. A process according to claim 1 wherein the alkyl halide is a butylhalide.

5. A process according to claim 1 wherein the molar ratio of alkylhalide to magnesium-tin alloy is within the range from 2:1 to 8:1.

6. A process for producing halogen-free butyltin compounds whichcomprises reacting at a temperature not substantially above C. butylchloride with a magnesiurn-tin alloy in the presence of mercuricchloride and a reaction solvent selected from the group consisting oftetrahydrofuran, tetrahydropyran, alkyl substituted tetrahydrofuran andtetrahydropyran in which the alkyl substituent is attached to a carbonatom not adjacent to the oxygen atom, and mixtures thereof.

7. A process of producing halogen-free alkyltin compounds whichcomprises reacting at a temperature not substantially above 150 C. analkyl halide with a magnesium-tin alloy in the presence of the reactionsolvent tetrahydrofuran.

8. A process of producing halogen-free alkyltin compounds whichcomprises reacting at a temperature not substantially above 150 C. analkyl halide with a magnesium-tin alloy in the presence of the reactionsolvent tetrahydropyran.

9. A process of producing halogen-free alkyltin compounds whichcomprises reacting at a temperature not substantially above 150 C. analkyl halide with a magnesium-tin alloy in the presence of the reactionsolvent consisting of a mixture of tetrahydrofuran and tetrahydropyran.

10. A process of producing halogen-free alkyltin compounds whichcomprises reacting at a temperature not substantially above 150 C. analkyl halide with a magnesium-tin alloy in the presence of a reactionsolvent consisting of an alkyl substituted tetrahydrofuran in which thealkyl substituent is attached to a carbon atom not adjacent to theoxygen atom.

11. A process of producing halogen-free alkyltin compounds whichcomprises reacting at a temperature not substantially above 150 C. analkyl halide with a magnesium-tin alloy in the presence of a reactionsolvent consisting of an alkyl substituted tetrahydropyran in which thealkyl substituent is attached to a carbon atom not adjacent to theoxygen atom.

References Cited by the Examiner UNITED STATES PATENTS 3,085,102 4/63Yatagai et a1. 260429.7

FOREIGN PATENTS 713,727 8/54 Great Britain. 878,958 10/61 Great Britain.

TOBIAS E. LEVOW, Primary Examiner.

1. A PROCESS FOR LPRODUCING HALOGEN-FREE ALKYLTIN COMPOUNDS WHICHCOMPRISES REACTING AT A TEMPERATURE NOT SUBSTANTIALLY ABOVE 150*C. ANALKYL HALIDE WITH A MAGNESIUM-TIN ALLOY IN THE PRESENCE OF A REACTIONSOLVENT SELECTED FROM THE GROUP CONSISTING OF TETRAHYDROFURAN,TETRAHYDROPYRAN, ALKYL SUBSTITUTED TETRAHYDROFURAN AND TETRAHYDROPYRANIN WHICH THE ALKYL SUBSTITUENT IS ATTACHED TO A CARBON ATOM NOT ADJACENTTO THE OXYGEN ATOM AND MIXTURES THEREOF.